As background, transfer paper is generally used in applying graphics to textiles, ceramics, plastics, and various arts and crafts projects. A printer is first used to print an image on paper, and then a heat press can is used to vaporize the image onto the textiles, ceramics, plastics, and other types of surfaces. That's why it is called “transfer paper,” it is used in creating transfers. There are various ways to print transfer paper including, inkjet printing, dye sublimation, color laser, rotogravure printing, and offset printing.
Important to the current application, dye-sublimation printing is a digital printing technology using full color artwork that generally works with various substrates, including polyester and polymer-coated substrates. The process is commonly used for decorating apparel, signs and banners, as well as novelty items such as cell phone covers, plaques, coffee mugs, and other items with sublimation-friendly surfaces. The process involves sublimation, in which heat and pressure are applied to a solid (in this instance the sublimation dyes), turning it into a gas through an endothermic reaction without passing through the liquid phase.
In sublimation printing, unique sublimation dyes are may be transferred to sheets of sublimation transfer paper, for example, by a liquid gel ink generally through a piezoelectric print head. The ink is deposited on these high-release inkjet transfer papers, which are used for the next step of the sublimation printing process. After the digital design is printed onto sublimation transfer sheets, it is placed on a heat press along with the substrate (banner, cell phone cover, coffee mug, etc.) to be sublimated.
The transfer of the image from the transfer paper to the substrate requires a heat press process that is a combination of time, temperature and pressure. The heat press applies this special combination, which can change depending on the substrate, to “transfer” the sublimation dyes found on the transfer paper at the molecular level into the substrate. The most common dyes used for sublimation activate at 350 degrees Fahrenheit. However, a range of 380 to 420 degrees Fahrenheit is normally recommended for optimal color.
The end result of the sublimation process is a nearly permanent, high resolution, full color print. Because the dyes are infused into the substrate at the molecular level, rather than applied at a topical level (such as with screen printing and direct to garment printing), the prints will not crack, fade or peel from the substrate under normal conditions.
Sublimation transfer paper is an important part of the sublimation process. Thus, the quality and characteristics of that paper is also important. Currently, sublimation transfer paper is specific to the type of ink systems that would be used to print the sublimation dyes. In other words, different types of sublimation transfer paper were needed for use with water, oil, and solvent based ink systems to obtain desirable results. Thus, if a printer used all three ink systems, it also needed three different types of sublimation transfer paper, which was inconvenient for many reasons, including the need and expense to stock the separate papers, and the time necessary to change between paper-types.
Another disadvantage with current sublimation transfer papers is that the sublimation coatings are only applied to the top of the paper after the paper is created. This causes inconsistent blooms for the sublimation inks, which leads to inconsistency of color. Also, when sublimation coatings are applied to the top of the paper after the paper is created, it causes an increase in cockling to the paper, which increases the distance that the print head needs to be from the paper, which lessens the detail in the print.
The present invention seeks to solve the prior shortcomings of sublimation transfer paper and their coatings. The present invention discloses a new and novel dye sublimation transfer paper and process of making that paper. The present invention is the first digital sublimation transfer paper that can be printed on with sublimation dispersible base inks, having a water base, oil base, and a solvent base. The same color quality is achieved regardless of the ink base utilized. Therefore, there is no need to use alternative types of paper for alternative types of ink.
As noted above a major shortcoming of the existing sublimation transfer paper is that the coatings are applied after the paper formation is complete, generally as a wet laminate coating to the top of an already existing sheet. The present invention overcomes this shortcoming by applying the coating as part of the paper manufacturing process. As a result, the coating is integrated or married into the paper. This marrying of paper and coating has at least two major benefits. First, it causes consistent blooms for the sublimation inks, which leads to consistency of color. Second, the integration of the coating into the paper causes less cockling of the paper which allows the print head on the printer to be closer to the paper, thus, allowing better detail in the print. Both of these benefits should also lead to the use of at least 25% less printer ink. These benefits allow for a new and very unique sheet that will not only provide extremely bright, saturated colors, but also outstanding detail with reduced ink loads. This new paper allows the dye to become part of the coating, yet keeps it from swelling, which improves resolution in the transfer. The resulting paper is also humidity stable and fast-drying.